Fuel injection nozzle for dme fuel, and diesel engine including the fuel injection nozzle for dme fuel

ABSTRACT

An existing diesel engine vehicle of light oil fuel is enabled to run as a diesel engine vehicle using DME as fuel without exchanging a whole diesel engine and at very low cost and easily. The shape of a tip part  21  of a needle valve  2  is set by a center diameter L3 for regulating a minimum flow path area at full lift of a fuel injection nozzle  1 , a seat diameter L2 of a seat part  211  coming in contact with a valve seat part  33  and blocking communication with a fuel injection hole  31 , and a shaft diameter L1, and a tip end angle is about 92 degrees. The center diameter L3 is set to φ2.5 mm, the seat diameter L2 is set to φ3.0 mm, and the shaft diameter L1 is set to φ3.25 mm. The ratio of the center diameter L3 and the seat diameter L2 is L3/L2=2.5 mm/3.0 mm=about 0.833, and the ratio of the seat diameter L2 and the shaft diameter L1 is L2/L1=3.0 mm/3.25 mm=about 0.92.

TECHNICAL FIELD

The present invention relates to a fuel injection nozzle for DME fuel ina diesel engine using DME (DiMethyl Ether) as fuel.

BACKGROUND ART

A conventional fuel injection nozzle of a diesel engine using light oilas fuel includes, for example, a needle valve 2 as shown in FIG. 9. Asshown in FIG. 10, in a state where an outer peripheral surface of a tippart 21 of the needle valve 2 is seated on a valve seat part 33,communication of light oil fuel to a fuel injection port 31 of a nozzlebody 3 is blocked and a fuel injection nozzle 1 is put in a valve closedstate (for example, see JP-A-11-13576). The tip part 21 of the needlevalve 2 has such a shape that the ratio of a shaft diameter L1 and aseat diameter L2 of a seat part 211 coming in contact with the valveseat part 33 becomes L2/L1=0.60 to 0.75. Besides, it has such a shapethat the ratio of the seat diameter L2 and a center diameter L3 forregulating a minimum flow path area at full lift of the needle valve 2becomes L3/L2=0.35 to 0.60. As shown in FIG. 11, the needle valve 2 islifted in a direction denoted by reference character B, the flow path isconstructed of a space produced by separation of the tip part 21 of theneedle valve 2 from the valve seat part 33, and the fuel injectionnozzle 1 is put in a valve open state. The needle valve 2 is regulatedso that a minimum flow path area d at a time when it is lifted by a liftamount denoted by reference character D and is put in a full lift statebecomes an optimum flow path area by the center diameter L3.

High pressure light oil fuel supplied from a not-shown injection pump, acommon rail and the like flows into the inside of the valve seat 33, andis sprayed into a combustion chamber of the diesel engine from the fuelinjection hole 31 as indicated by reference character C. The highpressure light oil fuel sprayed into the combustion chamber is burned byspontaneous ignition due to mixture with high temperature and highpressure air.

As stated above, the combustion of the diesel engine is performed insuch a way that the fuel is sprayed into the high temperature and highpressure air, and the spontaneous ignition is caused by the mixture ofthe air and the fuel. However, atmospheric pollution by the dieselengine becomes a problem in recent years, and as measures against theatmospheric pollution, attention is paid to using DME, whose exhaust isclean, as fuel instead of the light oil. Since the DME fuel has a highcetane number and compression ignition is possible, it can be used asfuel of the diesel engine. Besides, since smoke and SOx are notcontained at all in the exhaust gas, it is harmless to human beings, andthere is no influence on the destruction of the ozone layer and thegreenhouse effect. Further, since it is relatively easily synthesizedfrom various raw materials other than oil, it can be mass-produced at alow cost comparable to light oil.

Accordingly, from social demands such as the environmental problem dueto the exhaust gas, the exhaustion of oil resources, and the necessityof fuel diversification against an unexpected oil crisis, there is ahigh possibility that it is realized in near future that traveling andpossession of an existing diesel engine vehicle using light oil as fuelis prohibited by regulations. Besides, at the present moment, except forDME, there is nothing more valuable than DME as an alternate fuel of adiesel engine substituting for the light oil, and a diesel engine systemof the DME fuel is currently at an advanced stage of development, andaccordingly, it can be said that the light oil is substituted by DME asthe fuel of the diesel engine before too long.

However, as described above, although DME has many merits as the fuel ofthe diesel engine, as compared with the light oil, energy obtained froma same amount of fuel is low, and accordingly, when the amount of fuelinjection is the same as that in the case of the light oil, an engineoutput becomes lower than that in the case of the light oil. Thus, aconventional diesel engine using light oil as fuel can not be useddirectly as a diesel engine using DME as fuel. In the case where adiesel engine using DME as fuel is designed and manufactured from thefirst, it is sufficient if the amount of fuel injection is set so that aspecified engine output can be obtained by the DME fuel. However, in anexisting diesel engine vehicle using light oil as fuel, in case themounted whole diesel engine must be exchanged with a diesel engine ofDME fuel, it takes very high cost, labor, and time, and this can not besaid to be realistic. Accordingly, even if a diesel engine vehicle ofDME fuel is put to practical use, the replacing of existing light oilfuel diesel engine vehicles is not smoothly carried out, and by that,the spread of the diesel engine of DME fuel is much delayed, and thereis a fear that measures against the worrying destruction of theenvironment and global warming are delayed, and the exhaustion of oilresources is hastened.

DISCLOSURE OF THE INVENTION

The invention has been made in view of such circumstances, and itsobject is to enable an existing diesel engine vehicle of light oil fuelto run as a diesel engine vehicle using DME as fuel without exchangingthe whole diesel engine, and at very low cost and easily.

In order to achieve the above object, according to a first aspect of theinvention, a fuel injection nozzle for DME fuel, which is mounted ineach combustion chamber of a light oil fuel diesel engine and is fordriving the light oil fuel diesel engine by using DME fuel, includes anozzle body having a fuel injection hole with a total injection holearea to attain an injection amount of the DME fuel which enables anengine output comparable to light oil fuel to be obtained, and a needlevalve provided to be capable of reciprocating to the fuel injectionhole, and is characterized in that the needle valve is lifted from astate where a tip part of the needle valve is seated on a valve seatpart of the fuel injection hole and from a state where the fuelinjection hole is closed, and the tip part of the needle valve isseparated from the valve seat, so that a fuel flow path of the DME fuelfrom an inside of the nozzle body to the fuel injection hole isconstructed, and the fuel flow path with a flow path area to enable anengine output characteristic comparable to the light oil fuel withrespect to a lift amount of the needle valve to be obtained by the DMEfuel is constructed.

In order to obtain the engine output comparable to the light oil fuel,it is necessary to increase the fuel injection amount with respect tothe lift amount of the needle valve. Then, first, the total injectionhole area of the fuel injection hole formed in the nozzle body, which isan injection port for injecting the DME fuel into the combustionchamber, is increased. That is, the total injection hole area of thefuel injection hole is made to have such a size that the injectionamount of the DME fuel from the fuel injection hole enables the engineoutput comparable to the light oil fuel to be obtained. By that, the DMEfuel whose amount enables the engine output comparable to the light oilto be obtained can be injected into the combustion chamber.Incidentally, in order to obtain the engine output comparable to thelight oil fuel by using the DME fuel, the fuel injection amountapproximately twice as large is required, and therefore, it is necessarythat the fuel injection hole with the total injection hole areaapproximately twice as large or larger is formed the in nozzle body.

The fuel flow path of the DME fuel from the inside of the nozzle body tothe fuel injection hole, which is constructed in such a manner that theneedle valve is lifted and the tip part of the needle valve is separatedfrom the valve seat part, has the flow path area to enable the engineoutput characteristic comparable to the light oil fuel with respect tothe lift amount of the needle valve to be obtained by using the DMEfuel. Thus, in the diesel engine designed to use the light oil as thefuel, the engine output comparable to the light oil fuel can be obtainedby using the DME fuel without changing the outer shape of the fuelinjection nozzle, the outer diameter of the needle valve and the like.Accordingly, when the fuel injection nozzle of the existing dieselengine designed to use the light oil as the fuel is exchanged for thefuel injection nozzle for DME fuel, the existing diesel engine of thelight oil fuel can be directly driven as the diesel engine using DME asfuel.

By this, according to the fuel injection nozzle for DME fuel of thefirst aspect of the invention, when the fuel injection nozzle of theexisting diesel engine designed to use the light oil as the fuel isexchanged for the fuel injection nozzle for DME fuel, the existingdiesel engine of the light oil fuel can be directly driven as the dieselengine using DME as fuel. Accordingly, the operation and effect that theexisting diesel engine vehicle of the light oil fuel can be made to runas the diesel engine vehicle using DME as fuel without exchanging thewhole diesel engine, and at very low cost and easily.

According to a second aspect of the invention, in the first aspect, thefuel injection nozzle for DME fuel is characterized in that the tip partof the needle valve has a shape that a ratio of a center diameter L3 forregulating a minimum flow path area and a seat diameter L2 of a seatpart seated on the valve seat part is L3/L2=0.70 or higher.

The ratio L3/L2 of the center diameter and the seat diameter, which isset to about 0.35 to 0.6 in the conventional diesel engine using lightoil as fuel, is set to 0.70 or higher. That is, the difference betweenthe center diameter and the seat diameter becomes small, and as thevalue of the center diameter/the seat diameter approaches 1, the size ofthe center diameter approaches the seat diameter, and the intervalbetween the seat part coming in contact with the valve seat part and thecenter diameter becomes short. Accordingly, since the center diameterinevitably becomes larger than the convention needle valve, the positionof the center diameter in the valve seat part in the state where theseat part is seated on the valve seat part is positioned at an innerperipheral surface of the valve seat part having an inner diameterlarger than a conventional one. Accordingly, the inner diameter of theinner peripheral surface of the valve seat part, together with thecenter diameter, constituting the minimum flow path area at full liftbecomes large, and by that, the minimum flow path area regulated by thecenter diameter at full lift can be increased.

By this, according to the fuel injection nozzle for DME fuel of thesecond aspect of the invention, since the ratio L3/L2 of the centerdiameter and the seat diameter is set to 0.70 or higher, the minimumflow path area at full lift regulated by the center diameter can beincreased, and by that, the foregoing operation and effect of theinvention of the first aspect can be obtained.

According to a third aspect of the invention, in the second aspect, thefuel injection nozzle for DME fuel is characterized in that the tip partof the needle valve has the shape that a ratio of a shaft diameter L1 ofthe needle valve and the seat diameter L2 is L2/L1=0.85 or higher.

The ratio L2/L1 of the shaft diameter and the seat diameter, which isset to about 0.60 to 0.70 in the conventional diesel engine using lightoil as fuel, is set to 0.85 or higher in the invention. That is, thedifference between the shaft diameter and the seat diameter becomessmall, and as the value of the seat diameter/the shaft diameterapproaches 1, the size of the seat diameter approaches the shaftdiameter. Accordingly, the seat diameter becomes larger than that of theconventional needle valve, and in proportion to that, the centerdiameter also becomes large inevitably. Accordingly, the position of thecenter diameter in the valve seat part and in the state where the seatpart is seated on the valve seat part is positioned at an innerperipheral surface of the valve seat part having a further large innerdiameter. Accordingly, the inner diameter of the inner peripheralsurface of the valve seat part, together with the center diameter,constituting the minimum flow path area at full lift becomes furtherlarge, and by that, the minimum flow area regulated by the centerdiameter at full lift can be further increased.

By this, according to the fuel injection nozzle for DME fuel of thethird aspect of the invention, since the ratio L2/L1 of the shaftdiameter and the seat diameter is set to 0.85 or higher, the minimumflow area at full lift regulated by the center diameter can be furtherincreased, and by that, the foregoing operation and effect according tothe invention of the second aspect can be obtained.

According to a fourth aspect of the invention, in any one of the firstto third aspects, the fuel injection nozzle for DME fuel ischaracterized in that the fuel injection hole has a shape that the totalinjection hole area is 0.6 mm² or larger.

Since the total injection hole area of the fuel injection nozzle of theconventional diesel engine using light oil as fuel is set to about 0.3mm² or smaller, when the total injection area is made 0.6 mm² or larger,the fuel flowing through the fuel injection hole can be increased twiceor more. Accordingly, it becomes possible to obtain the engine outputcomparable to or higher than the light oil fuel by using the DME fuel inwhich as compared with the conventional light oil fuel, approximatelyhalf engine output is merely obtained when the amount of fuel is thesame.

According to a fifth aspect of the invention, a diesel engine includes afuel injection nozzle for DME fuel according to any one of the first tofourth aspects.

According to the diesel engine of the fifth aspect of the invention, inthe diesel engine, especially in the existing diesel engine designed touse light oil as fuel, the foregoing operation and effect of any one ofthe first to fourth aspects of the invention can be obtained.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view showing a rough structure of a nozzle holderincluding a fuel injection nozzle for DME fuel according to theinvention.

FIG. 2 is a sectional view showing a rough structure of the fuelinjection nozzle for DME fuel according to the invention.

FIG. 3 is a perspective view showing outer appearances of a needle valveand a nozzle body of the fuel injection nozzle for DME fuel according tothe invention.

FIG. 4 shows the needle valve of the fuel injection nozzle for DME fuelaccording to the invention, in which FIG. 4(a) is a front view of theneedle valve and FIG. 4(b) is a front view in which a tip part of theneedle valve is magnified.

FIG. 5 is a sectional view in which a part of the fuel injection nozzlefor DME fuel according to the invention is magnified and shown.

FIG. 6 is a sectional view in which the part of the fuel injectionnozzle for DME fuel according to the invention is magnified and shown,and shows a state where the needle valve is lifted from a valve closedstate shown in FIG. 5.

FIG. 7 is a graph schematically showing a characteristic of a flow patharea with respect to a lift amount of the needle valve of the fuelinjection nozzle for DME fuel according to the invention.

FIG. 8 shows another embodiment of a fuel injection nozzle for DME fuelaccording to the invention, in which FIG. 8(a) is a front view of aneedle valve, and FIG. 8(b) is a front view in which a tip part of theneedle valve is magnified.

FIG. 9 shows a needle valve of a conventional fuel injection nozzleusing light oil as fuel, in which FIG. 9(a) is a front view of a needlevalve, and FIG. 9(b) is a front view in which a tip part of the needlevalve is magnified.

FIG. 10 is a sectional view in which a part of the fuel injection nozzleof a diesel engine using light oil as fuel is magnified and shown.

FIG. 11 is a sectional view in which the part of the fuel injectionnozzle of the diesel engine using light oil as fuel is magnified andshown, and shows a state where the needle valve is lifted from a valveclosed state shown in FIG. 10.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, embodiments of the invention will be described withreference to drawings while a comparison is made to a conventional fuelinjection nozzle of a diesel engine using light oil as fuel.

FIG. 1 is a sectional view showing a rough structure of a nozzle holderincluding a fuel injection nozzle as “fuel injection nozzle for DMEfuel” according to the invention.

A fuel injection nozzle 1 is a long stem type hole nozzle, and isdisposed in each combustion chamber of a diesel engine by a nozzleholder 50. A DME fuel pressurized to a high pressure is introduced(reference character A) into a nozzle body 3 of the fuel injectionnozzle 1 from an inlet connector 53 through a filter 531. A nozzlespring 52 at an upper part of a push rod 51 regulates an injection startpressure of the fuel injection nozzle 1, and its adjustment is performedby an adjusting screw 54. Lubrication of a sliding part of the fuelinjection nozzle 1 is performed by part of the DME fuel, and the DMEfuel having performed the lubrication fills a receiving space of thenozzle spring 52, and is returned to a not-shown fuel tank from anoverflow part 55.

FIG. 2 is a sectional view showing a rough structure of the fuelinjection nozzle 1 according to the invention, and FIG. 3 is perspectiveview showing outer appearances of a needle valve 2 and the nozzle body 3of the fuel injection nozzle 1.

As indicated by an arrow of reference character A, the high pressure DMEfuel introduced from the inlet connector 53 into the inside of the fuelinjection nozzle 1 through the filter 531 fills the inside of the nozzlebody 3 through an oil storage chamber 32. The needle valve 2 is moved ina direction indicated by reference character B by the pressure of theDME fuel in the inside of the nozzle body 3 to open a valve, and the DMEfuel is injected from a fuel injection hole 31 into the combustionchamber as indicated by an arrow of reference character C.

FIG. 4 shows the needle valve 2 of the fuel injection nozzle 1 of theinvention, in which FIG. 4(a) is a front view of the needle valve 2, andFIG. 4(b) is a front view in which a tip part 21 of the needle valve 2is magnified. FIG. 5 is a sectional view in which a part of the fuelinjection nozzle 1 is magnified and shown.

The needle valve 2 has a substantially cylindrical shape, and the tippart 21 has a substantially right circular cone shape. The shape of thetip part 21 is set by a center diameter L3 for regulating a minimum flowpath area of the fuel injection nozzle 1 at full lift, a seat diameterL2 of a seat part 211 coming in contact with a valve seat part 33 andblocking communication with the fuel injection hole 31, and a shaftdiameter L1, and a tip part angle is abut 92 degrees. The centerdiameter L3 is set to φ2.5 mm, the seat diameter L2 is set to φ3.0 mm,and the shaft diameter L1 is set to φ3.25 mm. The ratio of the centerdiameter L3 and the seat diameter L2 is L3/L2=2.5 mm/3.0 mm=about 0.833,and the ratio of the seat diameter L2 and the shaft diameter L1 isL2/L1=3.0 mm/3.25 mm=about 0.92.

In the fuel injection nozzle 1 of a valve closed state, the outerperipheral surface of the tip part 21 of the needle valve 2 urged in astate where the injection start pressure is regulated by the springforce of the nozzle spring 52 is seated on the valve seat part 33 of thenozzle body 3 as an inlet of the fuel injection hole 31 as shown in thedrawing. Then, the needle valve 2 is lifted by the pressure of apredetermined amount of high pressure DME fuel sent from an injectionpump and the like, so that the tip part 21 of the needle valve 2 isseparated from the valve seat part 33 to form a valve open state, andthe DME fuel is sent from between the tip part 21 of the needle valve 2and the valve seat part 33 to the fuel injection hole 31.

For information, in the needle valve 2 of the fuel injection nozzle 1 ofthe diesel engine using light oil as fuel shown in FIG. 9, the centerdiameter L3 is set to 1.1 mm, the seat diameter L2 is set to φ2.2 mm,and the shaft diameter L1 is set to φ3.25 mm. The ratio of the centerdiameter L3 and the seat diameter L2 is L3/L2=1.1 mm/2.2 mm=0.50, andthe ratio of the seat diameter L2 and the shaft diameter L1 is L2/L1=2.2mm/3.25 mm=about 0.68. Besides, as shown in FIG. 10, since the light oilfuel can produce an engine output larger than the DME fuel when the sameamount of fuel injection is used, the total injection hole area of thefuel injection hole 31 formed in the nozzle body 3 is set to be smallerthan the total injection hole area of the fuel injection hole 31 of thefuel injection nozzle 1 according to the invention.

FIG. 6 is a sectional view in which a part of the fuel injection nozzle1 of the invention is magnified and shown, and shows a state where theneedle valve 2 is lifted from the valve closed state shown in FIG. 5.

The needle valve 2 is moved in the direction of the arrow denoted byreference character B and is lifted to a position of a maximum liftamount D, and at a time point when a full lift state occurs, an area ofa portion where an interval between the tip part 21 of the needle valve2 and the valve seat part 33 becomes minimum is a minimum flow path aread. Accordingly, a flow path area formed of the minimum flow path area dbetween the outer peripheral surface of the tip part 21 and the valveseat part 33 is a minimum flow path area. Besides, a maximum value ofthe fuel injection amount is determined by the total injection hole areaof the fuel injection hole 31. Incidentally, in this embodiment, themaximum lift amount D at full lift of the fuel injection nozzle 1 is setto about 0.25 mm.

Here, as compared with the case of the fuel injection nozzle 1 of thediesel engine using light oil as fuel shown in FIG. 11, first, the sizeof the fuel injection hole 31 of the nozzle body 3 of the fuel injectionnozzle 1 according to the invention is formed to be larger, and by that,the total injection hole area is set to become approximately twice aslarge. This is because, as described before, in order to obtain the sameengine output as the light oil fuel by using the DME fuel, a fuelinjection amount larger than the light oil fuel becomes necessary.Accordingly, by setting the total injection hole area of the fuelinjection hole 31 to be larger than that in the light oil fuel, theengine output comparable to the light oil fuel can be obtained by theDME fuel.

Besides, in the tip part 21 of the needle valve 2, the ratio L3/L2 ofthe center diameter L3 and the seat diameter L2 is set to be as large asabout 0.833 in the fuel injection nozzle 1 of the invention, while it isset to 0.50 in the conventional fuel injection nozzle 1 of the dieselengine using light oil as fuel. Besides, the ratio L2/L1 of the seatdiameter L2 and the shaft diameter L1 is set to be as large as about0.92 in the fuel injection nozzle 1 of the invention, while it is set toabout 0.68 in the conventional fuel injection nozzle 1 of the dieselengine using light oil as fuel. By that, the minimum flow path area d ofthe fuel injection nozzle 1 of the invention at full lift isapproximately twice as large as that of the conventional fuel injectionnozzle 1 of the diesel engine using light oil as fuel.

As stated above, in order to obtain the fuel injection amount necessaryfor the DME fuel, the ratio L3/L2 of the center diameter L3 and the seatdiameter L2 is made 0.7 or higher and about 0.833 in this embodiment,and the ratio of L2/L1 of the seat diameter L2 and the shaft diameter L1is made 0.85 or higher and about 0.92 in this embodiment, so that theminimum flow path area d at full lift can be made the area approximatelytwice as large. Besides, by setting the hole diameter of each of thefuel injection holes 31 such that the total injection hole area becomesapproximately twice as large, the fuel injection amount of the fuelinjection nozzle 1 can be set to be approximately twice as large. Bythat, it is possible to obtain the fuel injection amount of the DME fuelwhich enables the engine output comparable to the light oil to beobtained.

FIG. 7 is a graph schematically showing a characteristic of a flow patharea with respect to a lift amount of the needle valve 2 of the fuelinjection nozzle 1 of the invention.

The graph indicated by a solid line is the graph of the fuel injectionnozzle 1 of the invention, and the graph indicated by an alternate longand short dash line is the graph of the fuel injection nozzle 1 of thediesel engine using light oil as fuel. An area denoted by referencecharacter E1 is the total injection hole area of the fuel injectionnozzle 1 of the diesel engine using light oil as fuel, and an areadenoted by reference character E2 is the total injection hole area ofthe fuel injection nozzle 1 of the invention. The flow path area(vertical axis of the graph) is increased as shown in the drawing inproportion to the lift amount (horizontal axis of the graph) of theneedle valve 2, and the flow path area characteristic of the needlevalve 2 with respect to the lift amount is determined by the ratio L3/L2of the center diameter L3 of the tip part 21 and the seat diameter L2,the ratio L2/L1 of the seat diameter L2 and the shaft diameter L1, andthe total injection hole area of the fuel injection hole 31. As isapparent from the graph, in the fuel injection nozzle 1 of theinvention, the flow path area with respect to the lift amount of theneedle valve 2 is larger than that of the fuel injection nozzle 1 of thelight oil fuel at a substantially constant ratio.

In this embodiment, the total injection hole area E2 of the fuelinjection nozzle 1 of the invention is set to the total injection holearea approximately twice as large as the total injection hole area El ofthe fuel injection nozzle of the diesel engine using light oil as fuel,so that the engine output characteristic comparable to the light oilfuel can be obtained by the DME fuel. The flow path area with respect tothe lift amount of the needle valve 2 is also set so that the flow patharea approximately twice as large can be obtained. Accordingly, the DMEfuel approximately twice as large as the light oil with respect to thelift amount of the needle valve 2 can be supplied to the combustionchamber of the diesel engine, and according to that, the total injectionhole area of the fuel injection hole 31 is also set to be approximatelytwice as large, so that the total injection hole area of the fuelinjection hole 31 does not become a bottle neck.

In this way, in the diesel engine designed to use light oil as fuel,when only the fuel injection nozzle is changed to the fuel injectionnozzle 1 of this invention, the engine output characteristic comparableto the light oil fuel can be obtained by the DME fuel without changingthe outer shape of the fuel injection nozzle, the shaft diameter of theneedle valve 2, and the like. Thus, the existing diesel engine vehicleof the light oil fuel can be made to run as the diesel engine vehicleusing DME as fuel at very low cost and easily.

Besides, as another embodiment, in addition to the first embodiment, itis possible to cite one in which a fuel injection amount of DME fuel isfurther increased. FIG. 8 shows another embodiment of a fuel injectionnozzle for DME fuel according to the invention, in which FIG. 8A is afront view of a needle valve 2, and FIG. 8B is a front view in which atip part of the needle valve 2 is magnified.

Since a part (portion denoted by reference character 2 a) of a shaft ofthe needle valve 2 is smaller than a shaft diameter L1 and has the samediameter as a seat diameter L2, an interval to a nozzle body 3 becomeswide by that, and a flow rate of DME fuel can be increased. Accordingly,it is possible to expect an effect that a diesel engine designed to uselight oil as fuel can be driven at an engine output comparable to orhigher than light oil by using DME fuel.

Incidentally, the invention is not limited to the above embodiments, andvarious modifications can be made within the scope of the inventionrecited in the claims. For example, the invention can be carried outalso in a hole nozzle which is not a long stem type, and it is needlessto say that those are also contained in the scope of the invention.

According to the invention, the existing diesel engine vehicle of thelight oil fuel can be made to run as the diesel engine vehicle using DMEfuel as fuel without exchanging the whole diesel engine, and at very lowcost and easily.

INDUSTRIAL APPLICABILITY

The present invention can be used as a fuel injection nozzle for DMEfuel in a diesel engine using DME (DiMethyl Ether) as fuel.

1. A fuel injection nozzle for DME fuel, which is mounted in eachcombustion chamber of a light oil fuel diesel engine and is for drivingthe light oil fuel diesel engine by using DME fuel, comprising: a nozzlebody having a fuel injection hole with a total injection hole area toattain an injection amount of the DME fuel which enables an engineoutput comparable to light oil fuel to be obtained; and a needle valveprovided to be capable of reciprocating to the fuel injection hole,characterized in that the needle valve is lifted from a state where atip part of the needle valve is seated on a valve seat part of the fuelinjection hole and from a state where the fuel injection hole is closed,and the tip part of the needle valve is separated from the valve seat,so that a fuel flow path of the DME fuel from an inside of the nozzlebody to the fuel injection hole is constructed, and the fuel flow pathwith a flow path area to enable an engine output characteristiccomparable to the light oil fuel with respect to a lift amount of theneedle valve to be obtained by the DME fuel is constructed.
 2. A fuelinjection nozzle for DME fuel according to claim 1, characterized inthat the tip part of the needle valve has a shape that a ratio of acenter diameter L3 for regulating a minimum flow path area and a seatdiameter L2 of a seat part seated on the valve seat part is L3/L2=0.70or higher.
 3. A fuel injection nozzle for DME fuel according to claim 2,characterized in that the tip part of the needle valve has the shapethat a ratio of a shaft diameter L1 of the needle valve and the seatdiameter L2 is L2/L1=0.85 or higher.
 4. A fuel injection nozzle for DMEfuel according to claim 3, characterized in that the fuel injection holehas a shape that the total injection hole area is 0.6 mm² or larger. 5.A diesel engine comprising a fuel injection nozzle for DME fuelaccording to claim 3 or 4.